RNA editing is a molecular process in which the base of a RNA molecule is altered by specific enzymes. In the following example, Cytosine (C) is changed to Uracil (U).
Figure 5-A-9. RNA editing of the apo-B gene.
In mammals, the apo-B gene is expressed in both hepatocytes (liver cells) and
intestinal epithelial cells. However, in liver cells, its product is a 500 kD
protein called Apo-B100 whereas in intestine cells its product is a smaller protein
called Apo-B48. The Apo-B100 is produced without RNA editing, but the Apo-B48 is
synthesized from an mRNA whose sequence has been altered by a specific enzyme. This enzyme changes a codon, CAA, in the middle of the original mRNA
to the stop codon UAA, thereby causing early termination of the protein synthesis.